The sodium-dependent glucose cotransporter (SGLT) allows transport of Na+ which goes according to concentration gradient to occur, and at the same time, allows transport of glucose which goes against concentration gradient to occur. Currently, two important SGLT isoforms have been cloned and are known as SGLT1 and SGLT2. SGLT1 is located in the intestines, kidney, and heart, and regulates cardiac glucose transport through expression thereof. Due to being a high-affinity, low-capacity transporter, SGLT1 is responsible for only a portion of renal glucose reabsorption. On the contrary, SGLT2 is a low-affinity, high-capacity transporter which is predominantly located in apical domains of epithelial cells in the early proximal convoluted tubule. In healthy individuals, over 99% of plasma glucose which is filtered in the renal glomeruli is reabsorbed, and less than 1% of total filtered glucose is excreted in the urine. It is estimated that 90% of renal glucose reabsorption is promoted by SGLT2 and the remaining 10% is mediated by SGLT1 in the late proximal straight tubule. Genetic mutation of SGLT2 does not have any particular adverse effects on carbohydrate metabolism. However, increased renal glucose secretion of about 140 g/day is caused depending on mutation. According to human mutation studies, SGLT2 has been a subject of therapeutic studies because it is estimated that SGLT2 is responsible for most renal glucose reabsorption.
US Laid-open Patent Publication No. 2015/0152075 discloses a compound having a diphenylmethane moiety which has an inhibitory activity on SGLT2, and a method for producing the same. The document discloses that the diphenylmethane derivative compound is effective for the treatment of diabetes in view of the fact that the diphenylmethane derivative compound exhibits an excellent inhibitory effect on human SGLT2 activity and significantly reduces urinary sugar excretion in animals as compared with Dapagliflozin which is well known as an SGLT2 inhibitor. In addition, US Laid-open Patent Publication No. 2014/0274918 discloses a diphenylmethane derivative which is effective as a dual inhibitor for sodium-dependent glucose cotransporter 1 (SGLT1) and sodium-dependent glucose cotransporter 2 (SGLT2).
In Example 172 of US Laid-open Patent Publication No. 2015/0152075 or the like, a method for producing a diphenylmethane compound c28 in the same manner as in the following Reaction Scheme 1 is disclosed.

However, according to the conventional method for producing the compound c28, a linear synthesis method such as forming a pentagonal ring in an aglycone group after being coupled with a glucose group is employed. In a case of such a linear synthesis, due to a complicated pathway, a low final yield is obtained. Besides, in a case where synthesis of a substituent of the glucose group or a cyclopropylbenzyl group which is bonded to dihydrobenzofuran goes wrong in the middle, or the substituent or cyclopropylbenzyl group is intended to be changed to another, there is inconvenience of having to go through the synthesis thereof again from the beginning. In addition, even for a process of synthesizing a cyclopropyl group of the compound c28, the process is carried out by cyclizing olefin through a Simon-Smith reaction at the end of the synthesis pathway, so that a yield varies greatly depending on a state (purity, anhydrous, or the like) of a reagent (diethyl zinc, solvent) and the like, and a reaction concentration.
In view of the above, the present inventors have discovered that a diphenylmethane derivative can be produced efficiently by a convergent synthesis method in which the respective main groups are separately synthesized and then coupled to each other, rather than the conventional linear synthesis method, and therefore, have completed the present invention.